Capillary underfill and mold encapsulation method and apparatus

ABSTRACT

A method of packaging a die includes attaching the die to a substrate; underfilling the space between the die and the substrate with a first material, and placing a second material in contact with at least a portion of the die and the substrate after underfilling the space between the die and substrate with the first material. A system includes a semiconductor package having a substrate, a die attached to the substrate, an underfill material positioned between the die and the substrate, and a molding material in contact with at least a portion of the substrate and the die. A heat sink is also in thermal contact with the semiconductor package.

FIELD OF THE INVENTION

The present invention relates generally to apparatus and methods forpackaging a device. More particularly, it relates to the capillaryunderfill and mold encapsulation process used for packaging a device.

BACKGROUND OF THE INVENTION

Typically a large number of semiconductor devices are formed on wafers.The semiconductor devices are formed by repeating a number of basicoperations on a wafer. The basic operations include layering,patterning, doping, and heat processing. The final semiconductor formedhas many layers of material and includes as many as 10,000 or moreindividual transistors. Rather than make each semiconductor deviceindividually, a number of devices are formed on a single wafer. Theentire wafer is subjected to the basic operations discussed above inorder to form hundreds of semiconductor chips or devices. Typically,after the semiconductor devices are formed, the semiconductor devicesare tested and sorted. Next, the wafer is sliced and diced so that eachindividual semiconductor device is separated from the others formed onthe wafer.

The individual semiconductor devices are formed on fragile material. Asa result, the individual semiconductor devices are packaged, in part forphysical protection. Packaging also dissipates the heat from thesemiconductor and provides leads between the individual chip or die andan exterior portion of the package. The leads allow for electricalconnection between the chip or die and a printed circuit board or otherdevice.

There are many different types of packages. One common package is a flipchip which has a series of bumps or balls or leads formed in an array ona surface of the flip chip. The flip chip is attached to a substrateduring packaging. The flip chip includes an inner layer dielectric (ILD)where the devices associated with the flip chip are formed. One methodof packaging includes attaching the flip chip or die to the substrateand then encapsulating the flip chip or die in plastic or epoxy. Part ofthis packaging method includes a molded underfill (MUF) where theplastic or epoxy is forced into the gap between the flip chip and thesubstrate. A high clamping force is placed on top of the flip chip ordie and a high transfer pressure is applied during the MUF process. TheILD is a fragile, thin film layer. The high clamping force and the hightransfer pressure causes the ILD to crack during the MUF process. Cracksin the ILD result in failures of the flip chip. In some instances, thesefailures may be latent failures which manifest themselves only aftermanufacture. Of course part failures are never desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.However, a more complete understanding of the present invention may bederived by referring to the detailed description when considered inconnection with the figures, wherein like reference numbers refer tosimilar items throughout the figures and:

FIG. 1 is schematic cutaway view of a semiconductor package, accordingto an embodiment of the invention.

FIG. 2A is schematic cutaway view of a semiconductor package at aninitial stage of packaging, according to an embodiment of the invention.

FIG. 2B is schematic cutaway view of a semiconductor package after acapillary underfill is placed between the die and the substrate,according to an embodiment of the invention.

FIG. 2C is schematic cutaway view of a semiconductor package aftermolding around at least a portion of the substrate and the die,according to an embodiment of the invention.

FIG. 3 is a flow chart of a method for forming a semiconductor package,according to an embodiment of the invention.

FIG. 4 is a flow chart of a method for forming a semiconductor packagewherein the backside surface of the die is devoid of a second, moldedmaterial, according to another embodiment of the invention.

FIG. 4 is a flow chart of a method for forming mold encapsulation of asemiconductor package, according to yet another embodiment of theinvention.

FIG. 5 is a schematic view of a system, according to an embodiment ofthis invention.

FIG. 6 is a method of forming a system, according to an embodiment ofthis invention.

FIG. 7 is a method for forming a semiconductor package, according to anembodiment of this invention.

FIG. 8 is a schematic cutaway view of a semiconductor package, accordingto another embodiment of the invention.

FIG. 9 is a flow chart of a method for forming a semiconductor package,according to an embodiment of this invention.

FIG. 10 is a flow chart of a method, according to an embodiment of thisinvention.

FIG. 11 is a schematic diagram of a computer system that can be used tocontrol the apparatus for attaching the semiconductor package and curinga material in contact with the package, according to an embodiment ofthis invention.

FIG. 12 is a block diagram of a computer-readable medium that includesan instruction set therein, according to an embodiment of thisinvention.

The description set out herein illustrates the various embodiments ofthe invention and such description is not intended to be construed aslimiting in any manner.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which are not necessarily to scale, which form apart hereof, and in which is shown, by way of illustration, specificembodiments in which the apparatus and methods can be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice them, and it is to be understood that theembodiments can be combined, or that other embodiments can be utilizedand that procedural changes can be made without departing from thespirit and scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope is defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views.

FIG. 1 is schematic cutaway view of a semiconductor package 100,according to an embodiment of the invention. The semiconductor packageincludes a substrate 110, a die 120 attached to the substrate 110. Thedie 120 includes an inner layer dielectric (ILD) layer 121 where thedevices associated with the die 120 are formed on a wafer beforesingulating the wafer into individual dies. An underfill material 130 ispositioned between the die 110 and the substrate 120. A molding materialor molding compound 140 contacts at least a portion of the substrate 110and the die 120. In some embodiments of the invention, the underfillmaterial 130 positioned between the die 120 and the substrate 110 isdifferent than the molding material or molding compound 140. The die 120includes a frontside surface 122 near the substrate 110, a backsidesurface 124, and four sidewall surfaces 126, 127, 128 and one not shown.In some embodiments, the molding material or molding compound 140contacts the four sidewall surfaces 126, 127, 128 and one not shown. Inother embodiments of the invention, the molding material or moldingcompound 140 contacts the four sidewall surfaces 126, 127, 128 and onenot shown and does not contact the backside surface 124 of the die 120.In other words, the backside surface 124 of the die 120 is devoid of themolding material or molding compound 140.

FIGS. 2A-2C show various schematic cutaway views during the formation ofthe package 100 shown in FIG. 1. FIG. 2A is schematic cutaway view of asemiconductor package 100 at an initial stage of packaging, according toan embodiment of the invention. Initially, the die 120 is attached tothe substrate 110 by reflowing the solder associated with a set ofsolderballs 220 attached to the die 120. The die and substrate areheated until the solderballs 220 are in a liquid state. The solderballs220 of the die 120 are positioned in an array. A similar array of padsis set forth on the substrate 110 so that when the solderballs 220 arereflowed, the solder attaches to the pads of the substrate 110, therebyelectrically connecting the solderballs 220 to the pads of the substrate110. This is generally referred to as chip attach and electricallyattaches the die 120 to the substrate 110. After chip attach there is aspace or gap between the frontside surface 122 of the die 120 and thesubstrate 110. The solder balls 220 bridge the gap in the form of anarray, but do not totally fill the gap. The ILD 121 is fragile and issubject to cracking if certain forces are placed on the die 120 andspecifically on the backside surface 124 of the die 120. An underfill130 can be formed in one of several ways. However, a capillary underfill130 generally minimizes the force on the die 120 and therefore minimizesthe risk of cracking the ILD 121 within the die 120. FIG. 2B isschematic cutaway view of a semiconductor package after a capillaryunderfill 130 has been placed between the die 120 and the substrate 110.The underfill 130 provides strength to the die 120 since the gap betweenthe die 120 and the substrate 110 is filled. Of course, in otherembodiments of the invention, the underfill may be done under pressure,especially if the die 120 is considered capable of withstanding thecorresponding forces without cracking the ILD.

The capillary underfill 130 is cured and then at least a portion of thedie 120 and the substrate 110 are encapsulated with a molding materialor compound 130. FIG. 2C is a schematic cutaway view of a semiconductorpackage 100 after molding around at least a portion of the substrate 110and the die 120, according to an embodiment of the invention. Themolding material or molding compound 130, as shown in FIG. 2C, contactsthe four sidewall surfaces 126, 127, 128 and one not shown and does notcontact the backside surface 124 of the die 120, as well as a portion ofthe underfill material 130. As shown in FIG. 2C, the backside surface124 of the die 120 is devoid of the molding material or molding compound140.

FIG. 3 is a flow chart of a method 300 for forming a semiconductorpackage, according to an embodiment of the invention. The method 300 forforming a semiconductor package includes initially attaching the die orchip, as depicted by reference numeral 310. The die is attached to thesubstrate in the die attach step 310. A prebake 312 is then done afterattaching the die to the substrate. After a prebake, a capillaryunderfill material is placed between the die and the substrate, asdepicted by reference numeral 314. Once the capillary underfill 314 isaccomplished, the capillary underfill area where the material that isused in the capillary underfill is cured, as depicted by referencenumeral 316. After the capillary underfill is cured, a plasma etch takesplace, as depicted by reference numeral 318. The next step is moldencapsulation 320 with a molding material or molding compound. The moldmaterial or molding compound is curable and, therefore, after the moldencapsulation step 320, the mold compound or mold material is cured, asdepicted by reference numeral 322.

FIG. 4 is a flowchart of a method 400 for a mold encapsulation of asemiconductor package, according to yet another embodiment of theinvention. Initially a film is placed on the backside surface of thedie, as depicted by reference numeral 410. The film that is used is ahighly compressible film such as a Teflon film or PTFE. Such highlycompressible films are available from specialty polymer companies, suchas DUPONT E I DE NEMOURS & CO, DuPont Building, 1007 Market Street,Wilmington, Del. 19898, USA. A force is then applied to the film, asdepicted by reference numeral 412. The back side surface of the die canthen be compressed or a force can be applied to the backside of the diesince the die has previously been under filled using a capillaryunderfill or other underfill. The process of underfilling stabilizes thedie and the ILD within the die so that by applying a force to the film412, the result will not be cracking or failure of the ILD within thedie. Next, the four sidewalls of the die are encapsulated with a secondmaterial. The force, or compression force, continues to be applied tothe film as the four sidewalls of the die are encapsulated. The film andthe compression force applied to it therefore allow encapsulation of thefour sidewalls of the die with the second material while leaving thebackside surface of the die devoid of the second material, as depictedby reference numeral 414. The next step is removing the film from thebackside surface of the die, as depicted by reference numeral 416. Theend result is a package that looks similar to the package found in FIGS.1 or 2C.

FIG. 5 is a schematic view of a system 500, according to an embodimentof this invention. The system 500 includes a semiconductor package 100having a substrate 110, a die 120 attached to the substrate, anunderfill material 130 positioned between the die 110 and thesubstratel20, and a molding material 140 in contact with at least aportion of the substrate 110 and the die 120. A heat sink 510 is also inthermal contact with the backside surface 124 of the semiconductorpackage 100. Some semiconductor packages 100, such as those associatedwith microprocessors, generate enough heat so that the heat sink 510must be used to remove heat from the semiconductor package and preventthe die from failing. The heat sink 510 is attached to the backsidesurface of the die. In some embodiments, a thermally conductivematerial, such as a thermal grease or thermal adhesive, is locatedbetween the backside surface 124 of the die 120 and the heat sink 510.The system 500 also includes a printed circuit board 520. Thesemiconductor package 100 includes a set of pins 115 is attached to theprinted circuit board 520. In some embodiments, the molding material 130contacts the four sidewall surfaces 126, 27, 128 and one not shown andthe backside surface.

FIG. 6 is a method 600 for forming a system 500, according to anembodiment of this invention. The method 600 of packaging a die includeselectrically connecting the die to a substrate 610, and underfilling thespace between the die and the substrate using a capillary underfill 612.The die includes a backside surface and four sidewall surfaces. Acompressible film is placed on the backside of the die 614. The film iscompressed, and the pressurized material or molding compound is thenplaced in contact on the four sidewall surfaces of the die 616. Thecompressible film is removed 618 and a heat transfer device is placed incontact with the die, thereby transferring heat from the backsidesurface of the die with a heat transfer device in contact with thebackside surface of the die 620. The pressurized material, in someembodiments, is a heated epoxy, phenolic or novalac resin. The film isremoved after the heated epoxy is cured.

FIG. 7 is a method 700 for forming a semiconductor package, according toan embodiment of this invention. The method 700 includes attaching thedie to the substrate 710 and underfilling the space between the die andthe substrate with a first material 712. A second material is placed incontact with at least a portion of the die and the substrate afterunderfilling the space between the die and the substrate with the firstmaterial, as depicted by reference numeral 714. This is followed bypartially encapsulating the die 716. Thus, according to this embodiment,the die is only partially encapsulated in this method.

FIG. 8 is a schematic view of a semiconductor package 800, according toanother embodiment of this invention. The semiconductor package 800includes a substrate 810 and a die 820. The die 820 is attached to thesubstrate 810. The die 820 includes an inner dielectric layer (ILD) 821where the device associated with the die are formed on a wafer beforesingulating the wafer into individual dies. An underfill material 830 ispositioned between the die 810 and the substrate 820. A molding materialor molding compound 840 contacts the substrate 810 and encapsulates thedie 820. The die includes a front side surface 822 positioned near thesubstrate 810, a backside surface 824, and four sidewall surfaces 826,827, 828 and one not shown. As shown in FIG. 8, the molding materialcontacts the four sidewall surfaces 826, 828, 827 and one not shown, aswell as the backside surface 824 of the die 820. Therefore, the backsidesurface 824 of the die 820 is covered with molding material or moldingcompound 840 in this particular embodiment of the invention.

FIG. 9 is a flowchart of a method 900 for forming a semiconductorpackage, according to an embodiment of this invention. The method 900includes attaching the die to the substrate 910 and underfilling thespace between the die and the substrate with a first material 912. Thesecond material is placed in contact with at least a portion of the dieand the substrate after underfilling the space between the die and thesubstrate with the first material, as depicted by reference numeral 914to encapsulate the die 916. The second material is placed in contactwith the backside surface 824, as well as the sidewall surfaces 826,827, 828 and one not shown of the die 820. Encapsulating the die isreferenced by reference numeral 916.

FIG. 10 is a flowchart of a method 1000, according to an embodiment ofthe invention. The method 1000 includes electrically connecting the dieto the substrate 1010, underfilling the space between the die and thesubstrate using a capillary underfill 1012, and placing a pressurizedmaterial in contact with at least a portion of the die and the substrateafter the capillary underfill 1014.

A method of packaging a die includes electrically connecting the die toa substrate, underfilling the space between the die and the substrateusing a capillary underfill, and placing a pressurized material incontact with at least a portion of the die and the substrate after thecapillary underfill. The die includes a backside surface and foursidewall surfaces. Placing a pressurized material in contact with atleast a portion of the die and the substrate after the capillaryunderfill includes encapsulating the backside surface and the foursidewall surfaces with the pressurized material. In some embodiments ofthe invention, the pressurized material is a heated epoxy, phenolic ornovalac resin. In some embodiments, the heated epoxy, phenolic ornovalac resin is a different material than a material associated withunderfilling the space between the substrate and the die. In someembodiments, placing a pressurized material in contact with at least aportion of the die and the substrate after the capillary underfillexcludes placing the pressurized material on the backside surface of thedie. In still other embodiments, placing a pressurized material incontact with at least a portion of the die and the substrate after thecapillary underfill includes placing a film on the backside of the die,and placing the pressurized material on the four sidewall surfaces ofthe die. In still other embodiments, placing a pressurized material incontact with at least a portion of the die and the substrate after thecapillary underfill further includes placing a film on the backside ofthe die, pressurizing the film, placing the pressurized material on thefour sidewall surfaces of the die, and removing the film. Thepressurized material, in some embodiments, is a heated epoxy. The filmis removed after the heated epoxy is cured. The method further includestransferring heat from the backside surface of the die with a heattransfer device in contact with the backside surface of the die.

A method of packaging a die includes attaching the die to a substrate;underfilling the space between the die and the substrate with a firstmaterial, and placing a second material in contact with at least aportion of the die and the substrate after underfilling the spacebetween the die and substrate with the first material. In someembodiments, the first material is a curable epoxy. In still otherembodiments, a capillary action of the first material is used inunderfilling the space between the die and the substrate. In otherembodiments of the invention, the second material is a heated epoxy,phenolic or novalac resin. In some embodiments of the invention, placinga second material in contact with at least a portion of the die and thesubstrate includes encapsulating the die. Placing a second material incontact with at least a portion of the die and the substrate includespartially encapsulating the die. Partially encapsulating the dieincludes placing a film on the backside surface of the die, applying aforce to the film, and encapsulating the four sidewalls of the die withthe second material while leaving the backside surface of the die devoidof the second material. The method also includes removing the film fromthe backside surface of the die. In some embodiments, placing a secondmaterial in contact with at least a portion of the die and the substrateincludes leaving the backside surface of the die devoid of the secondmaterial.

A computer system can be used to control packaging apparatus toimplement the methods 300, 400,600, 700, 900, and 1000 set forth above.FIG. 11 is a schematic diagram of a computer system 2000 that can beused to implement the methods 300, 400,600, 700, 900, and 1000. Thecomputer system 2000 may also be called an electronic system or aninformation handling system. The computer or information handling systemincludes a central processing unit 2004, a random access memory 2032,and a system bus 2030 for communicatively coupling the centralprocessing unit 2004 and the random access memory 2032. The informationhandling system 2002 also includes an input/output bus 2010 and severaldevices peripheral devices, such as 2012, 2014, 2016, 2018, 2020, and2022 maybe attached to the input output bus 2010. Peripheral devices mayinclude hard disc drives, magneto optical drives, floppy disc drives,monitors, keyboards and other such peripherals.

FIG. 12 is a block diagram of a computer-readable medium 1200 thatincludes an instruction set 1210 therein. The computer-readable mediumcan be any type of memory, a disk used for magnetic disk storage,optical disk storage, flash memory devices, or other machine-readablemedia. Media can also be read-only memory or random-access memory, whichis part of a hardware configuration for a computer system. Furthermore,the media can also include the internet, storage available to a server,or a transmission of any sort, connected or wireless, that is used totransmit the instructions to a computer system.

A computer program product for use with a computer system associatedwith a device such as a set of stations in a semiconductor packagingoperation, the computer program product includes a computer usablemedium that causes a computer to execute the methods and processes setforth in FIGS. 2-4 above. In other words, a set of instructions 910associated with the computer program product and executable by asuitably programmed information handling system and embodied in thecomputer usable medium causes the computer system 800 to execute themethods and processes set forth in FIGS. 2-4 and detailed in the aboveparagraphs.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A method of packaging a die comprising: electrically connecting thedie to a substrate; underfilling the space between the die and thesubstrate using a capillary underfill; and placing a pressurizedmaterial in contact with at least a portion of the die and the substrateafter the capillary underfill.
 2. The method of claim 1 wherein the dieincludes a backside surface and four sidewall surfaces, wherein placinga pressurized material in contact with at least a portion of the die andthe substrate after the capillary underfill includes encapsulating thebackside surface and the four sidewall surfaces with the pressurizedmaterial.
 3. The method of claim 2 wherein the pressurized material is adifferent material than a material associated with underfilling thespace between the substrate and the die.
 4. The method of claim 1wherein the pressurized material associated with placing a pressurizedmaterial in contact with at least a portion of the die is a differentmaterial than a material associated with underfilling the space betweenthe substrate and the die.
 5. The method of claim 1 wherein the dieincludes a backside surface and four sidewall surfaces, wherein placinga pressurized material in contact with at least a portion of the die andthe substrate after the capillary underfill excludes placing thepressurized material on the backside surface of the die.
 6. The methodof claim 1 wherein the die includes a backside surface and four sidewallsurfaces, wherein placing a pressurized material in contact with atleast a portion of the die and the substrate after the capillaryunderfill further includes: placing a film on the backside of the die;and placing the pressurized material on the four sidewall surfaces ofthe die.
 7. The method of claim 1 wherein the die includes a backsidesurface and four sidewall surfaces, wherein placing a pressurizedmaterial in contact with at least a portion of the die and the substrateafter the capillary underfill further includes: placing a film on thebackside of the die; pressurizing the film; placing the pressurizedmaterial on the four sidewall surfaces of the die; and removing thefilm.
 8. The method of claim 7 wherein the pressurized material is aheated epoxy and wherein the film is removed after the heated epoxy iscured.
 9. The method of claim 7 further comprising transferring heatfrom the backside surface of the die with a heat transfer device incontact with the backside surface of the die.
 10. A semiconductorpackage comprising: a substrate; a die attached to the substrate; anunderfill material positioned between the die and the substrate; amolding material in contact with at least a portion of the substrate andthe die.
 11. The semiconductor package of claim 10 wherein the underfillmaterial positioned between the die and the substrate is different thanthe molding material.
 12. The semiconductor package of claim 10 whereinthe die includes: a frontside surface near the substrate; a backsidesurface; and four sidewall surfaces, wherein the molding materialcontacts the four sidewall surfaces.
 13. The semiconductor package ofclaim 10 wherein the die includes: a frontside surface near thesubstrate; a backside surface; and four sidewall surfaces, wherein themolding material contacts the four sidewall surfaces and the backsidesurface is devoid of the molding material.
 14. The semiconductor packageof claim 10 wherein the die includes: a frontside surface near thesubstrate; a backside surface; and four sidewall surfaces, wherein themolding material contacts the four sidewall surfaces and the backsidesurface.
 15. A system comprising: a semiconductor package including: asubstrate; a die attached to the substrate; an underfill materialpositioned between the die and the substrate; and a molding material incontact with at least a portion of the substrate and the die; and a heatsink in thermal contact with the semiconductor package.
 16. The systemof claim 15 wherein the semiconductor package includes: a backsidesurface; and four sidewall surfaces, wherein the molding materialcontacts the four sidewall surfaces and the backside surface.
 17. Thesystem of claim 15 wherein the semiconductor package includes: abackside surface; and four sidewall surfaces, wherein the moldingmaterial contacts the four sidewall surfaces and the backside surface isdevoid of the molding material and wherein the heat sink is attached tothe backside surface of the die.
 18. The system of claim 17 furthercomprising a thermally conductive material located between the backsidesurface of the die and the heat sink.
 19. The system of claim 15 furthercomprising a printed circuit board wherein the semiconductor package isattached to the printed circuit board.
 20. The system of claim 15wherein the die of the semiconductor package is a microprocessor.
 21. Amethod of packaging a die comprising: attaching the die to a substrate;underfilling the space between the die and the substrate with a firstmaterial; and placing a second material in contact with at least aportion of the die and the substrate after underfilling the spacebetween the die and substrate with the first material.
 22. The method ofclaim 21 wherein the first material is a curable epoxy.
 23. The methodof claim 21 wherein a capillary action of the first material is used inunderfilling the space between the die and the substrate.
 24. The methodof claim 21 wherein the second material is a curable epoxy.
 25. Themethod of claim 21 wherein placing a second material in contact with atleast a portion of the die and the substrate includes encapsulating thedie.
 26. The method of claim 21 wherein placing a second material incontact with at least a portion of the die and the substrate includespartially encapsulating the die.
 27. The method of claim 26 wherein thedie includes a backside surface and at least four sidewall surfaces,wherein partially encapsulating the die includes: placing a film on thebackside surface of the die; applying a force to the film; andencapsulating the four sidewalls of the die with the second materialwhile leaving the backside surface of the die devoid of the secondmaterial.
 28. The method of claim 27 further including removing the filmfrom the backside surface of the die.
 29. The method of claim 21 whereinthe die includes a backside surface and at least four sidewall surfaces,wherein placing a second material in contact with at least a portion ofthe die and the substrate includes leaving the backside surface of thedie devoid of the second material.